1. Field of the Invention
The invention relates to a stand-up unit with a support and a stand-up mount which is articulated to the support and has a seat carrier carrying a seat, a backrest carrier carrying a backrest, a first lever parallelogram to hold the backrest upright both in the sitting position and in the standing position of the user, and means for moving the backrest to the trailing end of the seat during a change from the sitting position to the standing position, the first lever parallelogram having a first double-armed parallelogram lever. Stand-up units of this type are for example used in stand-up wheelchairs and therapy chairs.
2. State of the Art
Even the first designers of stand-up wheelchairs were confronted with the problem that a relative movement between the seat and backrest surfaces and the chair user's body can occur during standing-up. The resultant shear forces can lead to decubitus in the user of the chair. A relative movement between the chair and the user's body is produced when the axis of rotation of the seat does not correspond to the axis of rotation of the knee joint. In reality, the situation is somewhat more complex because the knee joint does not perform a pure rotational movement. On the contrary, in addition, a translatory movement also takes place. A relative movement also takes place between the user's back and the backrest when the axis of rotation of the backrest does not correspond to the axis of rotation of the knee joint.
In order to avoid the undesirable relative movements described hereinbefore, as early as in 1969 the inventor of one of the first stand-up wheelchairs had the idea of forming the seat and backrest by a large number of padded rolls (U.S. Pat. No. 3,589,769). However, these stand-up wheelchairs have not proven to be successful. Some 10 years later WO 79/00647 proposed lowering the footrest as the user of the chair stands up in order in this way to avoid an undesirable relative movement between the seat and the user's body. However, the lack of stability of the footrest, which is articulated to the stand-up mount roughly at the level of the user's knee and, somewhat further down, is connected in an articulated manner to the chassis by a connecting member, proved to be disadvantageous. In the stand-up wheelchair according to EP 0 815 822, this drawback is avoided in that the footrest has a shaft which is guided in the chassis. Many documents reveal that the stand-up wheelchairs described therein do not allow the user to stand fully upright. On the contrary, the user remains in a slightly oblique position in which he exerts forces on the seat and backrest. Many designs of known wheelchairs are dependent on forces of this type in order to avoid blockage at the dead centre or in the region close to the dead centre of the stand-up mechanism (U.S. Pat. No. 3,589,769, U.S. Pat. No. 4,623,194, DE 26 25 046, FR 2 529 456 and the corresponding EP 0 146 660, EP 0 815 822, EP 1 600 134).
As the patent literature also discloses, almost all the stand-up wheelchairs proposed in the last 30 years make use of the lowering of the footrest, although an undesirable relative movement between the seat and user of the chair is not always avoided (FR 2 529 456 and the corresponding EP 0 146 660, U.S. Pat. No. 4,623,194, EP 0 815 822 and EP 1 600 134). If, however, it is necessary to lower the footrest as the user stands up, this presupposes that the footrest must be arranged relatively high in the sitting position. The user of the wheelchair thus sits much higher in the wheelchair than a non-disabled person on a normal chair.
U.S. Pat. No. 4,054,319, U.S. Pat. No. 4,456,086 and U.S. Pat. No. 6,125,957 have already described stand-up wheelchairs in which the footrest is at the same height in the sitting and standing positions. However, in these examples, the footrest is also arranged relatively high on a chassis; in addition, undesirable relative movements are not in all cases avoided.
DE 26 25 046 describes a stand-up chair which can also serve as a therapy chair. The chair has a cam which can be adapted to the ideal stand-up movements of the patient. Together with a guide member and a limiting lever, this cam controls and limits the stand-up movement of the seat and backrest. The aim of this mechanism was to prevent almost all relative movements between the user's body and the surface of the chair. However, the described mechanism did not achieve this aim because the axis of rotation between the backrest and seat is arranged at a relatively great distance from the hip joint of the user of the chair. Furthermore, the use of cam discs has the drawback that they are subjected to a high degree of wear during operation. This stand-up chair and known stand-up wheelchairs have been found to have the further drawback that the seat surface presses the user of the chair forward as he stands up, the lower legs in the region of the knees being pressed with additional pressure against the knee holders which are necessary in most cases. This often causes an incorrect standing position. WO 03/026550 therefore proposes a mechanism to move the knee holders forward during the change from the sitting to the stand-up position. However, a mechanism of this type makes the stand-up chair more expensive.
EP 0 146 660 discloses a stand-up wheelchair having a chassis with a stand-up mount articulated thereto. The stand-up mount has a seat carrier with a backrest carrier. Furthermore, a first and a second lever parallelogram are provided. The first lever parallelogram holds the backrest carrier upright both in the sitting and in the standing position of the user. The second lever parallelogram is used to lower the footrest. For this purpose, the first lever parallelogram has a double-armed parallelogram lever which forms an arm part of the second lever parallelogram. As was previously mentioned, this stand-up wheelchair, like almost all the stand-up wheelchairs proposed in the last 30 years, makes use of the lowering of the footrest. This has the drawback that the wheelchair user sits much higher on a wheelchair of this type than a non-handicapped person on a usual chair. This has proven to be disadvantageous, for example, when sitting at a table where, on the one hand, there is the risk that the user's knees will knock the tabletop and, on the other hand, the user is sitting much too high for activities such as writing or eating.
The previously examined stand-up chairs provide an articulation at just two points. EP 1 716 834, on the other hand, describes an apparatus having a large number of members connected in an articulated manner. The members form an articulated system having an articulation at three points, i.e. not just an articulation in the region of the user's knee joints and in the region of his hip joints, but a further articulation also for his foot joints. A member, which at the level of the foot joints is articulated to a frame, is thus provided on each side of the apparatus. Springs and weights are provided in order to compensate for the user's weight (FIG. 4). Furthermore, it is proposed to pull the backrest upward via a cable pull by means of a cable pull which runs over two rolls and has a weight suspended therefrom. Another proposal suggests attaching weights to the members which are articulated to a frame at the level of the foot joints so as to be able to pivot forward and backward. The first-mentioned proposal, which provides a weight on a cable, is suitable only for stationary chairs, but not for movable stand-up wheelchairs. The second-mentioned proposal, attaching weights to the members at the level of the foot joints, is undesirable for stand-up wheelchairs because this increases the overall weight thereof. The proposal of articulating the stand-up mount to pivotable members, instead of to a stationary support, also makes the system according to EP 1 716 834 furthermore unattractive for use in stand-up wheelchairs. In stand-up wheelchairs, the stand-up mount is generally articulated to a stationary support which can be part of the chassis.
It is an advantage of the present invention to provide a stand-up unit which is suitable for stand-up wheelchairs and therapy chairs and at least substantially avoids the drawbacks described at the outset. In particular, almost no relative movement between the upper legs of the chair user and the seat is to take place as the user stands up and sits down. As little relative movement as possible should also take place between the back of the chair user and the backrest. The stand-up unit should allow the user to stand upright and also offer him secure support. The height of the armrest should also be in a position which is pleasant for the user of the chair, both when he is sitting and when he is standing. Finally, the stand-up unit should be as light as possible.
According to the invention, in a stand-up unit according to the type mentioned at the outset, this is achieved in that the first lever parallelogram has a second double-armed parallelogram lever, in that the arms of the two double-armed parallelogram levers form a second lever parallelogram with two further levers, in that the common pivot point of the two lever parallelograms is connected in an articulated manner to a first point of the footrest via a lever and in that the common pivot point of the aforementioned further levers of the second parallelogram is connected in an articulated manner to a second point of the footrest.
The formation according to the invention of the stand-up unit prevents almost all relative movements between the user's body and the seat as the user stands up, since the seat is raised as the user stands up. The fact that the footrest does not have to be lowered during the change from the sitting position to the standing position is particularly advantageous on use of the stand-up unit in stand-up wheelchairs. In stand-up wheelchairs, the footrest can be arranged relatively low in the sitting position, so that the user of the chair does not sit much higher than a normal chair user; this is advantageous particularly when eating or working at a table. In contrast to the system of EP 1 716 834, in the described stand-up unit, the stand-up mount is articulated not to pivotable members, but to a stationary support, as is also the case in most stand-up wheelchairs. This has the advantage that further measures, such as for example weights on pivotable members of this type, are not necessary, and the overall weight of the stand-up unit can thus be kept low.
In therapy chairs, the footrest can extend flat in relation to the ground. The footrest can also be dispensed with. However, in this case, the support is expediently formed so as to be height-adjustable in order to permit adaptation to the user. The fact that the legs of the user of the chair are not pressed intensively against the knee holders as he stands up is also advantageous. The knee holder therefore does not require a mechanism in order to prevent this. A further advantage of the invention consists in the fact that the stand-up mount is suitable for use with various types of chassis.
Depending on the state of the user's health, the stand-up unit can be used with or without a linear drive. Expediently, the linear drive is arranged between the support and the first lever parallelogram. Expediently, the first lever parallelogram has a third double-armed parallelogram lever, on the arm of which the backrest carrier is displaceable. Furthermore, the first double-armed lever is connected in an articulated manner to the backrest carrier by means of a rod. The backrest carrier is therefore moved downward as the user stands up, so that no relative movement takes place between the backrest and the user's back.
A linear drive, which can be actuated by the user for standing up and sitting down, can be provided between the footrest and the first lever parallelogram. A motor drive is not required for users having minor disabilities. However, it is in any case expedient to provide spring means in order to counteract the user's body weight.
A particularly advantageous formation of the stand-up unit makes provision for the lever, which is connected in an articulated manner to the footrest, to have a first spring joint element, for example what is known as a ROSTA element, which is coupled to the first lever parallelogram lever and for the lever to have a second spring joint element which is coupled to the footrest. In the sitting position, the spring elements are biased and strive to pivot the seat upward counter to the user's weight. Advantageously, the spring joint elements generate, after reaching a predetermined pivot position, a force which counteracts the further upward pivoting of the seat. This has the advantage that the joint play is cancelled and stand-up wheelchair ensures secure support for the user in the standing position. In contrast to most known stand-up wheelchairs, the user can stand fully upright.
Advantageously, the stand-up mount has two seat frames between which the seat, backrest and footrest are arranged. This produces a particularly stable design.